1. Field of the Invention
The present invention relates to a mixing/extruding apparatus, and a start-up method for a mixing/extruding apparatus.
2. Description of the Related Art
A mixer/extruder used for manufacturing resin pellets has a charging portion for resin, a mixing portion for feeding the charged resin while mixing the resin with a rotor, a screw, and the like, and an extruding portion for extruding the melt resin mixed into a melt state. A pelletizer such as an underwater cutting pelletizing device is coupled to an outlet part (on the downstream side) of the extruding portion, so that pelletizing to the pellets is performed with this pelletizer.
In such a mixer/extruder, by providing an electric motor for rotating and driving the rotor, the screw, and the like of the mixing portion, and a power supply device for supplying a drive power to this electric motor, a mixing/extruding apparatus is formed. As the electric motor, an electric motor having an optimum output is selected from outputs exceeding a few thousand kW to ten thousand kW in accordance with a type or a processing amount of the resin to be mixed.
Upon start-up of the mixing/extruding apparatus, the electric motor is started up, a small amount of the resin is next charged from the charging portion of the mixer/extruder, and then, the melt resin is taken out from an opening portion (diverter) provided on the near side of an outlet of the extruding portion to an exterior of the mixer/extruder, or the extruding portion and the pelletizer are separated, so that the melt resin is taken out from a die plate provided in the outlet of the extruding portion to the exterior of the mixer/extruder. After the melt state of the taken resin is confirmed, the diverter is closed and the pelletizer is coupled to the extruding portion, so that the mixing/extruding apparatus shifts to a continuous normal operation (for example, refer to Japanese Examined Patent Application Publication Nos. 2009-220486 and 2009-220333).
In recent years, since an increase in the processing amount is required, a large-sized mixer/extruder with a mixing chamber having a large inner diameter (diameter) is increasingly used. In this mixer/extruder, when a flow rate of the resin to be charged upon start-up is small, a retaining time of the resin is increased. Further, the resin is rotated at fixed high speed which is the same as the normal operation in the mixing chamber, so that shear force is applied to the resin by the number of times which is excessive with respect to a small charging amount of the resin.
Due to these factors, a temperature of the resin is increased more than necessary. If the mixing/extruding apparatus shifts to the normal operation while the resin is in such a state, a quality problem is caused in the melt resin in an actual normal operation or there is a problem that difficulty is created in a cutting operation of the pelletizer.
For such a reason, it is preferable to bring the flow rate of the resin to be charged upon the start-up as close to the normal operation as possible (to increase the flow rate). On the other hand, in a case where the resin taken out from the mixer/extruder is treated by a manual work, it is unfavorable to increase the flow rate with no reason. Thus, after the melt state of the resin taken out from the mixer/extruder is confirmed, in order to eliminate a need for the manual work in a case where the flow rate is large, there is a proposed method for conveying a large amount of the discharged resin to outdoors of a plant building or the like by a conveying device (for example, refer to Japanese Examined Patent Application Publication Nos. 2002-522253 and 2007-181949).
It should be noted that as one measure for avoiding the problems upon the start-up in the mixer/extruder as described above, there is a proposed method in which a small-sized electric motor for start-up is provided separately from an electric motor, this small-sized electric motor for the start-up is used for rotation and driving at low speed at the time of starting up a mixing/extruding apparatus, and the small-sized electric motor is switched to the electric motor when the mixing/extruding apparatus shifts to a normal operation, so that fixed-speed rotation and driving are performed at high speed by this electric motor (for example, refer to Japanese Examined Patent Application Publication Nos. 2008-30442 and 2009-51032).
In the method for conveying the resin taken out from the mixer/extruder to the outdoors of the plant building or the like by the conveying device disclosed in Japanese Examined Patent Application Publication Nos. 2002-522253 and 2007-181949, although a charging resin amount upon the start-up can be increased, an amount of the resin to be taken out is also large. Thus, there is a problem that a harmful influence on an environment is increased.
In the method in which the small-sized electric motor for the start-up is provided separately from the electric motor disclosed in Japanese Examined Patent Application Publication Nos. 2008-30442 and 2009-51032, a device configuration is enlarged and complicated due to the two electric motors. Thus, there is a problem that not only equipment cost but also manufacturing cost of pellets are eventually increased.